A power supply system disclosed in a patent document 1 is known for a conventional technology. This power supply system includes a power supply part attached to an electric device to supply electric power, and a power source circuit disposed in the electric device. When an AC adaptor is removed from a main body of the electric device, and the electric device is operated by a secondary battery in the electric device, the power supply system prevents generation of a short-circuit current from the secondary battery to the outside by short-circuiting of a power receiving terminal of the electric device.
The electric device main body constitutes a circuit that cuts off the secondary battery from the power receiving terminal based on a control signal inputted from the power supply part. When the control signal is zero, the secondary battery and the power receiving terminal are cut off so that the short-circuit current is not generated.